1. Field of the Invention
The present invention relates to a naphthalene derivative, a material for an organic electroluminescence device and an organic electroluminescence device using the same.
2. Description of Related Art
An organic electroluminescence device (hereinafter called as organic EL device), which includes an organic emitting layer between an anode and a cathode, has been known to emit light using exciton energy generated by a recombination of holes and electrons that have been injected into the organic emitting layer.
Such an organic EL device, which has the advantages as a self-emitting device, is expected to serve as an emitting device excellent in luminous efficiency, image quality, power consumption and thin design.
In applying an emitting material to an organic EL device, a doping method, according to which a dopant material is doped to a host material, has been known as a usable method.
In order to effectively generate exciton from injected energy and effectively convert exciton energy into light emission, an organic EL device is arranged such that the exciton energy generated in a host is transferred to a dopant, and that the dopant emits light.
Examples of such a host and dopant are such condensed aromatic compounds each having a naphthalene skeleton as disclosed in Document 1 (JP-A-2007-84485), Document 2 (JP-A-2006-151966), Document 3 (JP-A-2005-19219), Document 4 (JP-A-2005-8588), Document 5 (JP-A-2004-18510), Document 6 (WO2007/46658) and Document 7 (JP-A-2003-142267).
However, although there has been a demand for an organic EL device that is free from pixel defects and excellent in luminous efficiency, heat resistance and lifetime, no material for an organic EL device or no host material has been found usable for providing such an excellent organic EL device.
On the other hand, in order to enhance internal quantum efficiency and achieve higher luminous efficiency, a phosphorescence material that emits light using triplet exciton has been developed. Recently, there has been a report on an organic device using phosphorescence emission.
Since the internal quantum efficiency can be enhanced up to 75% or more (up to approximately 100% in theory) by using such a phosphorescence material, an organic EL device having high efficiency and consuming less power can be obtained.
However, although exhibiting much higher luminous efficiency, such a conventional phosphorescent organic EL device has such a short lifetime as to be practically inapplicable.